docs: def remove_isolated_nodes_op(graph):
      """Build a new graph excluding the isolated nodes.
  
      :param pybel.BELGraph graph: A BEL graph
      :rtype: pybel.BELGraph
      """
      rv = graph.copy()
      nodes = list(nx.isolates(rv))
      rv.remove_nodes_from(nodes)
      return rv